1. Field of the Invention
This invention relates, broadly speaking, to an improved soldering, fusing or brazing method. More specifically, and with reference to a preferred embodiment, this invention relates to an improved soldering method wherein the article on which a soldering operation is to be performed is heated to a temperature appropriate for the soldering operation by condensing thereon hot saturated vapors of specific fluids, the method being particularly useful for conducting a plurality of simultaneous soldering operations such as reflow soldering or wave soldering on a line of printed circuit boards.
2. Description of the Prior Art
The present invention is particularly applicable to operations such as soldering, fusing or brazing requiring the application of heat to the article upon which the operation is to be performed to raise its temperature.
Although the present invention is not to be construed as limited to soldering, its background is most readily understood in the context of soldering.
Soldering operations require that the elements to be soldered be heated to a temperature sufficiently high to melt solder thereon, the said elements being protected from oxidation during the soldering step.
Conventionally, the well-known soldering iron has been used, the elements to be soldered being provided with a coating of flux on those areas being soldered to prevent oxidation during the soldering step. The soldering iron technique is not well suited to rapid mass soldering operations in which, for example, a single printed circuit board may have many closely spaced connections to be soldered.
Numerous suggestions have been made to provide soldering methods improving upon the conventional soldering iron technique and adapted for mass soldering requirements.
Thus, U.S. Pat. No. 3,359,132 (1967) to Wittmann discloses a process for solder-coating printed circuit boards wherein a layer of peanut oil is floated on a bath of molten solder. A circuit board, which has been provided with a coating of flux, is suspended in close proximity to the surface of the hot peanut oil and is held in such position so as to be preheated by a combination of radiation and air convection. Thereafter, the board is lowered through the layer of hot peanut oil into the molten solder bath in which soldering now takes place.
Other prior art of interest is listed below:
U.S. Pat. No. 2,869,497 (1959) to Lehner PA1 U.S. Pat. No. 3,536,243 (1970) to Higgins PA1 U.S. Pat. No. 3,612,388 (1971) to Wegener PA1 U.S. Pat. No. 3,726,465 (1973) to Boynton .Iadd.
An article titled "Solvent Vapor Solder Reflow" by E. G. Dingman, IBM Technical Disclosure Bulletin, Vol. 13, No. 3, dated Aug. 1970, describes an application of a boiling solvent (such as that sold under the trademark FREON E-5 by E. I. Dupont de Nemours & Co.) to facilitate removal and resolder of electronic components during printed circuit board rework operations. The solvent condenses only on areas having a temperature lower than the boiling point of the solvent used. This releases the heat of vaporization and enables solder network operations with materials and components that are heat sensitive. The rapid and selective application of heat to small areas with high thermal conductivity is possible within a matrix of material which is heat sensitive and cannot tolerate at high temperatures. Such selective heating of small areas is cumbersome, tedious and uneconomical when applied to mass soldering, fusing and brazing operations. .Iaddend.